I am having problems with shutting down, when i click shutdown, it logs off, says its shutting down and turns the monitor off… BUT DOESNT DIE!

The computer just stays powered up for hours and hours… I have left it in this state for 3 days waiting to turn off… its not going to happen.

I was also having blue screens of death during installation of vista (until i removed 1 of the 2 DDR2 chips)

could the ram being dodgy also be stopping my shutdown

2.4Ghz Intel Core 2 Quad, 2gb Corsair XMS2, XFX 8600GTS SLi, Asus P5N32-E SLi PLUS, 600W Silverstone, Thermaltake Armor